In recent years, under the progress of information-oriented society, as symbolized by high-vision Braun tubes and high resolution display tubes, various types of flat panel displays such as plasma displays and color cathode ray tubes, such as color Braun tubes, have been undergoing a continuing increase in image size and contrast. In addition, it has become necessary to form increasingly minute pixels on the faceplate to form high-resolution screens.
Consequently, enhancements of various characteristics such as an increase in emission luminance and the enhancement of adhesion of phosphors onto the surface of the faceplate have been sought.
In phosphors, which have been used in panel displays, particles having a diameter of about 2 to about 7 μm, are used which have been developed for color cathode ray tubes. Further, the excitation wavelength of the aforesaid phosphors have not been developed which is optimized for each flat panel display. As a result, hereafter, enhancements of various characteristics are still being sought. Particularly, as the display is more detailed in the future, minute phosphor particles which exhibit high luminance are sought.
Conventional phosphors which have been prepared utilizing crystal growth through firing exhibit a relatively wide particle size distribution. Particualarly, when burned employing a large amount of fusing agents, phosphors which exhibit a normal distribution are prepared. When a phosphor layer is formed employing such phosphors, the presence of minute particles as well as coarse particles is not preferred, in order to prepare a denser phosphor layer which results in higher luminance. If desired, these minute particles as well as coarse particles are removed through a classification operation. However, such a classification operation results in a low efficient work which leads to a decrease in yield. Specifically, the formation of coarse particles adversely affects the yield of particles having the desired particle diameter. Further, it is impossible to remove such coarse particles with any degree of assurance.
Accordingly, in order to form a phosphor layer for high resolution cathode ray tubes, it is essential that unnecessary minute particles, and particularly coarse particles, are not formed during firing.
In order to overcome the aforesaid problems, Japanese Unexamined Patent Application Publication No. (JP-A) 2001-329262 describes a technique in which the crystal habit of phosphors is controlled so that minute particles, and particularly coarse particles, are not formed during firing.
Further, as the diameter of conventional phosphor particles decreases which are prepared utilizing crystal growth through firing, the resulting emission efficiency as well as emission luminance decreases. As a result, almost no phosphors are currently commercially available which exhibit sufficient emission efficiency as well as emission luminance at a particle diameter of at most 1 μm.
Several production methods for phosphors comprised of particles, having a diameter of at most 1 μm, have been disclosed. As is disclosed in JP-A 8-81676, particles having a diameter of at most 1 μm are obtained employing a classification operation, but with resulting problems such as a decrease in phosphorescence luminance as well as a decrease in the yield.
In each step of production method of phosphors, particle coagulation results in an increase in the resulting particle diameter and greatly hinders preparation of more minute particles incorporated in phosphors. However, few inventions can be found which relate to minimization of the aforesaid drawbacks. Only JP-A 6-306358 describes a sintering inhibitor. However, the resulting effects (being particle coagulation minimizing effects) have been found to be insufficient.